This project has two specific aims: 1) To study the role of oxygen free radical generation in compounding tissue injury following reperfusion of ischemic myocardium during early evolution of an acute myocardial infarct (AMI). Two experiments will attempt to define this role: a) Animals undergoing reperfusion will be treated or not treated with free radical scavengers (superoxide dismutase [SOD] and catalase) and the blood from the venous drainage of the ischemic area and ischemic tissue evaluated acutely for free radical by spin trapping and determining electron spin resonance spectra, and b) To determine the effects of oxygen free radical scavengers SOD and catalase (O2. and HzO2) and mannitol (OH-) on infarct size after 1 hour ligation and reperfusion. It may then be possible to improve on the acute treatment and decrease loss of muscle with AMI. 2) To attempt to produce coronary collateral circulation in baboons with intermittent acute and chronic ischemia. Collateral circulation is not normally present in humans or baboons. Humans with coronary disease develop collaterals frequently. We wish to determine that collaterals can be produced or recruited in this animal species without naturally occurring collaterals. We believe this will be important to compare such acquired collaterals with those in humans as the best model in animals for the study of the impact of collateral circulation on a variety of physiological states and treatment interventions.